Homeostasis

• homeostasis - maintaining a stable internal environment
• there are many automatic control systems in your body - including both nervous and hormonal communications
• what needs to be controlled is - body temperature, CO2 levels, blood glucose, water levels, urea concentration
• automatic control systems are made up of receptors, coordination centres and effectors
• negative feedback counteracts a change
• Receptor detects a stimulus ( level too high or low ) and sends a signal to the control centre which organises a response then the effector produces it
• stimulus - change in environment
• central nervous system - brain and spinal cord which is connected to the body by sensory and motor neurones
• sensory neurone - carry electrical impulses to CNS from receptors
• motor neurone - carry electrical impulses from the CNS to effectors
• if the CNS coordinates a response - stimulus, receptor, sensory neurone, CNS, motor neurone, effector, response
• synapse - a gap between 2 neurones
• nerve signals can be transferred by chemicals by diffusing across the synapse and makes new electrical signals
• reflex arc - stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector
• effectors can be a muscle or a gland
• hormone - a chemical secreted by a gland that travels in the blood
• pituitary gland - releases hormones that control other glands ( master gland )
• thyroid - produces thyroxine which controls metabolism, body temperature and heart rate
• adrenal gland - produces adrenaline which increases heart rate and blood flow ( fight or flight )
• pancreas - produces insulin and glucagon to regulate blood glucose levels
• ovaries - produce oestrogen and progesterone
• testes - produce sperm and testosterone
• insulin - lowers blood glucose levels
• glucagon - raises blood glucose levels
• oestrogen - thickens uterus lining
• progesterone - maintains thickness of uterus lining
• testosterone - controls puberty and sperm production
• nerves - fast acting, act for short time, act on specific area
• hormones - slow acting, act for long time, act on general area
• insulin - blood has too much glucose, insulin is secreted from pancreas, glucose moves from blood into liver and muscle cells, glucose is converted into glycogen in the liver, blood glucose levels decrease
• glucagon - blood has low glucose, glucagon is secreted from pancreas, glycogen is broken down to glucose, glucose enters bloodstream, blood glucose levels increase
• type 1 diabetes - pancreas produces very little or no insulin, the glucose must be removed ( usually by insulin injections )
• type 2 diabetes - person becomes resistant to their own insulin, blood glucose levels rise dangerously high, obesity and carcinogens increase the risk
• menstrual cycle - stage 1 - menstruation begins ( between 4 and 7 days ) stage 2 - uterus lining builds up again stage 3 - egg develops and is released stage 4 - wall of uterus thickens and stays thick for 2 weeks before breaking down again
• FSH - produced in pituitary gland, egg matures, stimulates oestrogen production in ovaries
• oestrogen - produced in ovaries, thickens uterus lining, stimulates release of LH, inhibits release of FSH
• LH - produced by pituitary gland, releases an egg
• progesterone - produced in ovaries, maintains thick uterus lining, inhibits release of LH and FSH
• barrier methods physically prevent an egg and sperm from meeting ( e.g condoms and femidoms )
• hormonal methods of contraception either kill the sperm or make the uterus unsuitable for fertilisation or make the conditions in the uterus inhabitable for sperm